As a new-generation light source, an LED has the advantages of energy saving, environmental protection, long life, diversified colors, stable beam, and high electro-optical conversion rate. It has become a trend to use the LED as a lighting source in recent years.
However, the LED light source still has some energy that cannot be converted into light energy and is discharged in a form of heat energy. When an LED lamp made from an LED light source is used to replace a fluorescent lamp or a high-pressure gas discharge lamp which requires great light intensity, if no power adaption adjustment function is provided based on an internal ambient temperature of the lamp, a large amount of heat energy will be generated inside the relatively closed lamp. Consequently, the internal temperature of the lamp is higher than a safe temperature. High temperatures may accelerate damage to the LED and reduce a service life of the LED lamp.
Therefore, it is necessary to provide a drive circuit that can adaptively reduce a drive current of the LED light source and reduce an output power and an internal temperature of the LED lamp when the internal ambient temperature of the LED lamp is excessively high, so as to realize the purpose of protecting the LED light source and extending a service life of the lamp.
A fluorescent light source or high-pressure gas discharge light source can be replaced with an LED light source via two methods. One is to develop a dedicated LED drive circuit specifically based on the characteristics of LED devices; and the other is to directly use a ballast that drives a fluorescent light source or high-pressure gas discharge light source to drive the LED light source. The ballast includes a magnetic ballast and an electronic ballast. The electronic ballast outputs a high-frequency current, while the magnetic ballast outputs a low-frequency current. However, the direct replacement may also cause the problem of an excessively high internal temperature of the lamp.
To meet this demand, it is necessary to provide a drive circuit that can extend a service life of an LED lamp while still using the original magnetic ballast.